This invention relates to the field of light emitting devices (LEDs), and in particular to the use of a pre-formed matrix leadframe to facilitate the packaging of light emitting devices.
Metallic leadframes are commonly used as a substrate for mounting and encapsulating light emitting elements and providing contacts for external connections to the light emitting element.
In this example embodiment, the light emitting element 140 includes two electrodes, one on its lower surface, and the other on its upper surface. The mounting of the light emitting element 140 on the surface area 115 provides contact to one of the electrodes of the light emitting element 140, and a bond wire 145 provides contact to the other of the electrodes of the light emitting element, as illustrated in
After the light emitting elements 140 are mounted and coupled to the leadframe 110, as illustrated in
Typically, silicone is used as the encapsulant 250, and may include dyes, scattering particles, or wavelength conversion material, such as phosphors, that enhance or modify the light emitted through the encapsulant 250. The dome shape of the encapsulant 250 provides a hemispherical pattern to the light emitted from the encapsulated device; other shapes may be used to provide different emission patterns.
An advantage of the illustrated pattern in the leadframe 110 is that each of the cut points 130 (X) on the islands (150, 160 in
After singulation, the contact pads 105, 106 are folded outward along line 270, so that the pads 105, 106 lie parallel to the light emitting surface of the singulated device, as illustrated in
Although the above packaging process is fairly efficient, it requires quite a few steps, and the tie-bar removal and folding of the pads 105, 106 after the packaging may introduce stress fractures, thereby reducing the yield of the process. The tie-bar removal after encapsulation also exposes the remnants of the clipped electrodes that extend below the encapsulant.
Of particular note, the process is limited to a single row of devices being fabricated at the same time, which, in combination with the reduced yield caused by the post-encapsulation folding of the pads, substantially limits the efficiency of the process.
It would be advantageous to provide a simpler process for packaging light emitting devices using a leadframe. It would advantage to reduce defects caused by folding the tabs of light emitting devices after encapsulation. It would be advantageous to increase the number of light emitting devices that can be packaged at the same time.
To better address one or more of these concerns, in an embodiment of this invention, a leadframe is formed that simplifies the packaging of light emitting elements and/or eliminates the need for stress-inducing folding after encapsulation. In particular, the folding of the contact tabs for surface mounting is performed prior to the mounting and encapsulation of the light emitting devices on the leadframe. In an example embodiment, the leadframe may be formed so that an array, or matrix, of light emitting elements may be packaged during a single packaging process.
In an example embodiment, the leadframe is folded along at least four fold lines to pre-form the leadframe such that the contact pads for the light emitting device lie in a plane that is parallel to the surface area for mounting the light emitting element. After this folding, the light emitting elements are mounted on the leadframe, coupled to the contact pads, then encapsulated. The leadframe is then sliced to provide individual encapsulated (packaged) light emitting devices that are suitable for mounting on a surface, such as a printed circuit board, via the contact pads. Because the folding is performed prior to the mounting and encapsulation of the light emitting element, the encapsulated light emitting element is not subject to the stresses associated with the folding of the leadframe.
Because the contact pads are pre-folded to lie in a common plane, the patterns for the light emitting devices may be arrayed in two dimensions, forming a matrix of LED metal patterns, thereby increasing the number of light emitting devices that may be packaged at the same time, compared to the single row of light emitting devices discussed above.
The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:
Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.
In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the concepts of the invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. In like manner, the text of this description is directed to the example embodiments as illustrated in the Figures, and is not intended to limit the claimed invention beyond the limits expressly included in the claims. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
In this example, the light emitting element 140 of
As contrast to the prior art profile of the leadframe 110 at
Of particular note, as contrast to the prior art leadframe 110, this compound folding of the leadframe 310 is performed before the mounting and encapsulation of the light emitting element 140.
For ease of illustration, the light emitting element 140 is illustrated as being visible above the lead frame 310, although in a preferred embodiment, the surface area 315 of the leadframe 310 may be depressed at the locale of the light emitting element 140, to provide the aforementioned reflective cup for reflecting light that may be emitted from the sides of the light emitting element 140.
Only two devices 300 are illustrated in
By appropriate design of the LED metal patterns 301 in the leadframe 310, along with forming the compound folds 410A-B, 470A-B before attaching and embedding the light emitting elements 140, the complexity of the singulation process is significantly reduced, as compared to the prior art process illustrated in
In this example, the alternative hole pattern 520 of
Although only a 3×4 {each hole pattern defines two LED metal patterns 501) replication of the hole pattern 520 is illustrated in
The vertical dashed lines indicate the fold lines for forming the compound fold that places the contact pads 505, 506 of the LED metal patterns in a plane parallel to the surface area 615 upon which the light emitting elements 140 will subsequently be mounted. The resultant profile is illustrated below the plan view of the leadframe 610.
Light emitting elements 140 are picked and placed upon the surface area 615 of the compound folded leadframe 610, and subsequently encapsulated, as illustrated in
A planar view of the resultant singulated device is illustrated in
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.
For example, it is possible to operate the invention in an embodiment wherein the LED metal patterns are substantially different from the example patterns 301, 501 illustrated in the drawings. Any pattern may be used provided that the pre-folding of the leadframe to place the contact pads in a common plane does not substantially interfere with the isolation of the contact pads from one another, and does not substantially interfere with the singulation process. Placing the tie-bars that need to be removed for this isolation and singulation at the common plane of the contact pads after folding will generally suffice to avoid this interference.
Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2013/055842 | 7/16/2013 | WO | 00 |
Number | Date | Country | |
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61674883 | Jul 2012 | US |